I have about 300 users on my network, a mixture of XP, Vista, and 7. While the Vista and 7 machines have been very secure, I regularly have to clean viruses off of our XP machines. The most common infections are the fake AV apps, some of which are easy to remove, others more difficult.
Interestingly, most seem to pick them up using Google for search. Google is riddled with false and hijacked links that lead to infected sites. I have been moving people away from Google and have observed a reduction in infections.
